Fewer Mammography Screenings Are Safer in Women With Large Breasts or Implants

The risk of radiation-induced breast cancer is higher for women with large breasts or breast implants because extra screening views often increase their radiation exposure. These findings were reported in Annals of Internal Medicine (doi:10.7326/M15-1241). This comprehensive modeling study showed that the procedures would be safer for all women with biennial, instead of annual, screening mammograms and beginning at age 50 years instead of 40 years.

"For most women, the risks are very low," said Diana Miglioretti, PhD, professor of Biostatistics at University of California Davis School of Medicine and senior investigator at Group Health Research Institute in Seattle, Washington, and first author of the study.

"The one group I worry about is women with very large breasts who choose to be screened annually from ages 40 to 74 [years]. Most screening mammograms are 2 views per breast. Some women with large breasts need more than 4 views for a complete screening examination, increasing their exposure to ionizing radiation. In addition, the dose per view increases with compressed breast thickness, further increasing exposure."

The study found that annual screening of 100 000 women age 40 to 74 years induced an estimated 125 cases of breast cancer and led to 16 deaths while averting 968 deaths from breast cancer through early detection.

Among women with large breasts who required additional views for complete examination, who are estimated at 8% of the population, the risk for breast cancer was estimated to be higher, at 266 cancer cases and 35 deaths per 100 000 women screened. The radiation exposure was found to be 2.3 times higher for women with large breasts than for women with smaller breasts. These findings may also affect women with breast implants.

The risk for radiation-induced cancer was found to be reduced 5-fold by screening biennially and starting at age 50 years.

"For the majority of women, screening mammography is very safe," said Miglioretti. "And if you screen every other year between 50 and 74, that makes it safest."

Tomosynthesis may lessen radiation exposure, but it needs to be done with synthetic 2D views instead of occurring in addition to 2D digital mammography. The synthetic 2D images are not in wide use currently.

The authors emphasized that mammography screening is extremely safe and its benefits overwhelmingly exceed the radiation risk. They hope this study will help open conversations between women and their providers.

"Women need to have a dialogue with their primary care providers about when to start screening, when to stop screening, and how often to screen based on their personal values and the potential benefits and harms associated with each scenario," said Christoph Lee, MD, MSHS, associate professor of radiology at the University of Washington School of Medicine in St. Louis, Missouri, and coauthor of the study. "It's a really an important step."